JONES — OUTLIER OF UPPER TERTIARY IRONSAND. 



339 



laying before competent autliorities for having their affinities deter- 

 mined, and their characteristic markings described. 



Mr. Mitchell, in his notice in your July number, rightly places this 

 deposit; as also that of Cauterland Den, amongst the very lowermost 

 of our Forfarshire sandstones. The localities as well as the fossils 

 clearly indicate this. 



OlSr THE OUTLIER OF UPPER TERTIARY IRONSAND 

 ON THE jq"ORTH DOWNS OF KENT. 



By T. Rupert Jones, Esq., F.Gr.S., Assistant- Secretary of the 

 Geological Society of London. 



Having at times been asked questions about the " Fossiliferous 

 Ironsands" of the North Downs, which Mr. Prestwich described in 

 the Jommal of the Geological Society in 1858, vol. xiv., p. 322, &c., I 

 find that some little diagram appears to be wanted by amateur geo- 

 logists and general readers for the clearer demonstration of these 

 strata and their relations to the Chalk and the Drift. 



I beg, therefore, to offer you the accompanying diagram, illustrative 

 of the relationship of the so-called " Kentish Crag," agreeable, I 

 believe, to Mr. Prestwich' s views of the subject, as given in his 

 elaborate paper before mentioned. Having seen the ground at Len- 

 ham and Charing, to which Mr. Prestwich refers, and at the latter of 

 which places my friend Mr. W. Harris, F.G.S., had some sections 

 specially made, I feel the greater satisfaction in bearing testimony to 

 Mr. Prestwich' s careful working out of the w^hole question. 



In the diagram you will see the whole known succession of these 

 ii'onsand deposits at A, where such outhnes as those of Paddlesworth 

 and Yigo-Hill may be supposed to be represented ; and partial rem- 

 nants are seen at B, C, D, and E. At F and Fa may be discerned 

 instances of sandpipes which have imbibed the ironsands before the 

 changes at the surface led to the denudation of the ironsands off the 

 chalk, and the wearing of the Chalk into furrows and cavities, leav- 

 ing the clayish sands and gravel now known as " Drift," ot which G 

 represents the lower and H the upper portion. 



The sandpipes at Lenham, where the ironsand is found to be richly 

 fossiliferous, are such as are seen at F in the diagram, the broken 

 ironstone having sunk gradually in with the sinking superincumbent 

 beds as the cavity was slowly made in the Chalk, probably by the dis- 

 solution of the latter by means of percolating water.* At I the 



* See Mr. Prestwicli'B account of the formation of Sandpipes in the Chalk, 

 Jour. Geol, Soc, vol. xi., p. 64. 



